The purpose of a communications network is to transport information among a number of locations served by the network. The information to be transported is usually presented to the network in the form of time-domain electrical signals and may represent any combination of telephony, video, or computer data in a variety of formats. To transport such information, a typical communications network includes various physical sites and information conduits, i.e., links, that interconnect the stations. Each link carries information from one site to another, and each site has a line terminating equipment, which may comprise a multiplexing equipment, and a switching equipment.
The line terminating equipment (LTE) is an interface between a link and a site for transmitting and receiving information. The line terminating equipment transforms the electrical signals into a form of electrical, optical, or radio signals suitable for propagation through the link. Thus, each link has one end connected to a LTE at one site and the other end connected to another LTE located at another site.
Multiplexing (MUX) and demultiplexing (DMUX) equipment may be installed at a site to add or extract information from the network. Multiplexing is the process of combining several low data rate signals into a single high data rate signal for transmission through a communications link. Likewise, demultiplexing refers to the process of decomposing a high data rate signal into several low data rate signals. To transport the information across the network, an input signal is assigned to one or more channels of the multiplexing equipment. The signal is then processed, i.e., digitized, framed, encoded, frequency-justified, etc., and combined with other signals to form a composite signal. Upon reaching an intended destination, the information is extracted from the network by the inverse process of multiplexing, i.e., demultiplexing. In hierarchical multiplexing schemes, the MUX/DMUX equipment may partially demultiplex a received high data rate signal into several intermediate data rate signals for recombining with other signals prior to retransmission.
Switching equipment installed at a site redirects information signals onto selected outgoing links. The switching equipment installed at numerous sites within a network dynamically routes information through the network and, in effect, logically reconfigures the network.
Typically, network information is transported via links, such as electrical cables, microwave guides, and optical fiber conduits. Modulated light carried over fiber optic conduits offers several technical and economic advantages over other types of network links. The principal technical advantage is extremely high modulation bandwidth due to the high carrier frequency. Additional technical benefits are low signal attenuation and distortion, stable path characteristics, and immunity to induced signals. From the economic perspective, fiber optic network systems are more advantageous due to lower cost of manufacture and maintenance.
Synchronous Optical NETwork (SONET) is a standard than now dominates optical signal protocols, as well as network equipment and configurations. The SONET standard primarily specifies signal protocols and data rates to allow diverse equipment types to interoperate within the same network.
Despite the above advantages, however, some elements of fiber optic networks are expensive due to the technology in the line terminating equipment and the multiplexing equipment. The technology involved in implementing multi-gigabit-per-second paths inherently demands costliness in a line terminating equipment due to required precision of specialized equipment, production yields, development costs, etc. In terms of equipment placement, a line terminating equipment Add-Drop Multiplexer (ADM) allows for less costly implementations than another type of line terminating equipment Optical Line Terminating Multiplexer (OLTM) because an ADM may selectively add and drop portions of a passing multiplexed signal. Still, ADM equipment costs are not negligible. The placement of one or more ADMs at a site within a ring network is a design parameter of great importance as it affects network costs and limits flexibility to accomplish load balancing and new demand accommodation. Efficient placement of the equipment and distribution of load are, therefore, the two critical considerations in fiber optic networks.
Currently, a few software packages provide computer aided assessment of proposed physical layer designs and proposed routing of circuit demands. These include the SONET TOOLKIT by Bell Communications Research and the NetMate Fiber Center Planner by Northern Telecom. The software packages, assessing user-proposed layouts and routings, require user interaction to arrive at suitable network solutions. Furthermore, these packages do not provide for load balancing and equipment placement as two state variables upon which optimization is performed.
A need, therefore, exists for an apparatus and method of optimizing network arrangement in terms of load balancing and placement of equipment at network sites.